1999 LAND ROVER DISCOVERY relay

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-9
IDM outputs
The IDM receives the following signals from the BCU using the serial datalink to provide power outputs:
Description Signal type System
Unlock all doors enable Digital Locking/ Unlocking/ Alarm
Lock passenger and rear doors enable Digital Locking/ Unlocking/ Alarm
Superlock all doors enable Digital Locking/ Unlocking/ Alarm
Lock driver's door Digital Locking/ Unlocking/ Alarm
Rear fog lamps enable Digital Exterior lighting
Daylight running lamps enable Digital Exterior lighting
LH direction indicators enable Digital Direction indicators/ Hazard warning/ Alarm
RH direction indicators enable Digital Direction indicators/ Hazard warning/ Alarm
Gear position indicator illumination Digital Illumination
Headlamp main beam indicator disable Digital Illumination
Front wiper enable Digital Wipers and washers
Rear wiper enable Digital Wipers and washers
Rear window enable Digital Power windows
Shift lever solenoid enable Digital Automatic gearbox
Transfer box solenoid enable/ Alarm sounder
relayDigital Gearbox
Heated rear window enable Digital Heated screens

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-13
Anti-theft system
The BCU controls the logical switching operations for enabling and activating the anti-theft system. Features include:
lPerimetric protection – monitors the condition of doors and hinged panels.
lVolumetric protection – monitors the vehicle's interior space.
lRemote locking, superlocking and unlocking functions.
lEngine immobilisation and remobilisation.
lAdvanced mislock detection and automatic compensation.
lEKA code functions.
lCustomer configuration options.
lMarket configuration options.
Immobilisation
The immobilisation system comprises the following components:
lRF receiver.
lRF transmitter/ transponder.
lTransponder coil.
lBCU.
lDoor switches, door lock switches and bonnet switch.
lIDM.
lECM.
lStarter solenoid relay.
lStatus LED.
Alarm system
The alarm system comprises the following components:
lRF receiver.
lRF transmitter.
lBCU.
lIDM.
lDoor switches, door lock switches and bonnet switch.
lBattery backed-up sounder (BBUS).
lStatus LED.
On non NAS vehicles, power supply for the alarm sounder and the battery BBUS is provided through two relays in the
passenger compartment fuse box. Each of the coils of the alarm relays are directly connected to the IDM which
controls their operation under the direction of BCU signals received via the serial data bus.
On NAS vehicles, an audible warning is provided through operation of the vehicle horns. The BCU provides an earth
path for the coil of the horn relay to initiate vehicle horn operation.

+ ALARM SYSTEM AND HORN, DESCRIPTION AND OPERATION, Description.
Acclimatisation locking Disabled The vehicle cannot be locked if the ignition is on.
Enabled The vehicle can be locked if the ignition is on and the engine is
running.
Alarm tamper Disabled The security system LED does not flash when the security system has
been tampered with.
Enabled The security system LED flashes when the security system has been
tampered with.
Engine immobilised LED off The security system LED does not flash when the engine is
immobilised.
LED flash The security system LED flashes when the engine is immobilised.
Low battery warning Disabled The security system LED does not flash when the remote transmitter
battery is low.
Enabled The security system LED flashes when the remote transmitter battery
is low.
Emergency Key Access
(EKA)Disabled EKA is disabled.
Enabled EKA is enabled and the door locks operate electrically.
No unlock EKA is enabled, but the door locks do not operate electrically. Function Option Details

BODY CONTROL UNIT
86-3-14 DESCRIPTION AND OPERATION
Central Door Locking (CDL)
The BCU carries out the logic control operation for CDL. A CDL switch is mounted on the fascia panel and has two
inputs to the BCU, one for lock and one for unlock.
Door locking and unlocking can be performed using the remote transmitter in the keys and the receiver unit located
above the vehicle's headlining, behind the rear sunroof aperture. The receiver detects the signals sent from the
remote transmitter and sends a decoded signal to the BCU for processing.
Four methods of door locking are available:
lRemote handset locking.
lVehicle key locking.
lCDL switch locking.
lSpeed related locking.
Two security levels of door locking are available, CDL and Superlocking. The anti-theft alarm system works in
conjunction with the CDL system.
Electric windows and sunroof
The BCU controls the logical operations and the timing periods for the electric front windows. The rear windows are
hard-wired and the two electric sunroofs are controlled by a dedicated ECU which is enabled by the BCU.
The front windows are electrically operated using two rocker switches located in the centre console. Electric motors
are located in each of the front doors.
The rear windows are enabled by the IDM controlling the operation of the rear window relay located in the passenger
compartment fuse box.
Wipers and washers
The wiper and washer functions are controlled by the BCU and the IDM.
The front wipers and washers are operated from the switch stalk located on the right hand side of the steering column
and only operate when the ignition switch is in position I or II. The front wipers are operated by a motor located below
the windscreen plenum.

+ WIPERS AND WASHERS, DESCRIPTION AND OPERATION, Description.
The BCU controls the wiper motor frequency of operation via the IDM when intermittent wipe or wash is selected. The
front intermittent wipe option features five different intermittent delay periods. The shortest delay period is 3 seconds
and this is increased by 2 second increments up to a maximum delay of 11 seconds. The desired delay period for the
front wipers is set by the position of the rotary switch located on the wiper column stalk.
The rear wiper switch is located on the instrument pack cowl and is latched when pressed. The rear wiper electric
motor is located in the tail door. The rear wiper operation is controlled according to a programmed strategy via the
BCU and the IDM. The BCU also checks for a signal from either the reverse lamp switch located in the vehicle gearbox
(manual gearbox models) or the gear position switch (automatic gearbox models) for operating the rear wipers when
the vehicle is in reverse. The rear wiper and washer only operate when the ignition switch is in position II.
The front and rear washer pumps and the headlamp powerwash (where fitted) are also controlled through the BCU.
The washers are operated from electric pumps attached to the washer reservoir located in the left hand wheel arch.
The front wash switch is located on the wiper column stalk and is pulled towards the steering wheel to select the
washer function. When the front washers are operated, the wipers are also activated for three full cycles. The rear
wash switch is located on the instrument pack cowl. The BCU programme can be configured in one of two modes of
operation:
lNo wiper operation when the wash switch is pressed.
lWiper action after an initial delay of 400 ms.
Headlamp wash is activated by the BCU via the IDM and operates when the headlamps are on and the front washers
function is selected.

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-15
Electric seats
The BCU controls the logical operation of the electrically operated front seats. Two modes of operation are available:

+ SEATS, DESCRIPTION AND OPERATION, Description - electric seats.
lElectric seat adjustment is enabled if the ignition is on or the driver's door is opened for a short time period.
lElectric seat adjustment is enabled if the ignition is on and the driver's door is closed.
The seats are operated by four electric motors which control the seat cushion rear up/ down, the seat cushion front
up/ down, seat cushion forward/ rearward and seat squab recline. The electrically powered lumbar adjustment in each
seat is operated by a single motorised air pump and a solenoid located on the seat squab frame. The air pump inflates
a cushion in the seat squab and the solenoid operates a valve to deflate the cushion. The seat squab and cushion
may also contain heater elements to provide heated seat operation.
The switches for electrically operated seats are located either side of the centre console.
Direction indicators and hazard warning lamps
The direction indicator lamps are operated from a three position direction indicator switch on the left hand, steering
column stalk. The BCU only allows the lamps to work as direction indicators when the ignition switch is in position II.
The BCU also controls the lamps to operate as hazard warning lamps and as a visual warning for the anti-theft system,
in which cases all lamps flash simultaneously irrespective of the ignition switch position.
System control of the direction indicators and hazard warning lamps is provided by the BCU operating with the IDM
and two electronic relays located in the passenger compartment fuse box. The IDM and relays are integral parts of
the passenger compartment fuse box and cannot be serviced individually. The serial data bus is used for
communication of status and operation requests between the BCU, IDM and instrument pack.
The hazard warning lamps are operated from a latching pushbutton switch located on the fascia.
All direction indicator/ hazard warning lamp bulbs are rated at 5 Watts.
Headlamps
The BCU contains a feature which allow the vehicle headlamps to be turned on when the remote transmitter is
pressed (courtesy headlamps).
For markets with daylight running lamps, the BCU controls the logical operation of the daylight running lamps. Options
are daylight running lamps are on if the main beam headlamps are off, or the daylight running lamps are on with main
and dipped beam off and the gearbox not in Park.
Front fog lamps
For markets with front fog lamps fitted, the BCU controls the operation of the front fog lamps. Options can be selected
so that the fog lamps will operate with or without the headlamps on main beam.
Instrument pack
The BCU communicates with the instrument pack via a serial data bus.

+ INSTRUMENTS, DESCRIPTION AND OPERATION, Description.
lThe instrument pack provides the BCU and IDM with details of vehicle speed.
lSignals are provided from the IDM to the instrument pack and BCU when the direction indicator lamps are active.
lFor certain markets, the BCU provides a signal to the instrument pack for indicating when the transfer box is in
neutral.
lThe IDM can signal the instrument pack to illuminate a trailer warning lamp. This operates when the IDM senses
that the current drawn by the indicator circuit exceeds a preset threshold.
lThe odometer reading displayed on the instrument pack LCD screen is also stored in non volatile memory in the
BCU. Whenever the ignition is turned from position I to position II, the instrument pack and the BCU compare
their stored values.
lThe gear selector position is displayed on the instrument pack LCD screen under the direction of the BCU.
Starting
The starting system comprises a starter motor and solenoid located at the rear right hand side of the engine. A starter
relay controlled by the BCU is used to supply battery power for starter solenoid operation. The starter motor receives
its feed directly from the battery.

BODY CONTROL UNIT
86-3-16 DESCRIPTION AND OPERATION
Cruise control
The BCU processes several signals used for cruise control:
lWhen the brake pedal is pressed, a low voltage brake lamp signal is sent via the BCU to the cruise control ECU.
lThe gear position switch sends an input via the BCU to the cruise control ECU if the selector lever is in Park,
Neutral or Reverse.
lA voltage supply is fed from the BCU to the cruise control SET+ switch.
lA voltage supply is fed from the BCU to the cruise control RES switch.
On vehicles with automatic transmission, if the BCU receives an input from the gear position switch or the brake pedal
switch, the BCU sends a signal to the cruise control ECU to cancel or inhibit cruise control operation.

+ ENGINE MANAGEMENT SYSTEM - Td5, DESCRIPTION AND OPERATION, Description.

+ ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - cruise control.
Shift interlock (where fitted)
On automatic gearbox models, the BCU and IDM combine with an interlock relay located in the passenger
compartment fuse box to operate a shift interlock solenoid, so that the gear selector lever cannot be moved out of
Park until certain logical conditions have been satisfied. Operation of the interlock may be affected, if the battery
becomes discharged.

+ AUTOMATIC GEARBOX - ZF4HP22 - 24, DESCRIPTION AND OPERATION, Description.
Ignition key interlock (where fitted)
On automatic gearbox models, the ignition key interlock solenoid prevents removal of the ignition key from the ignition
switch when the transmission gear selector is not in the Park position. The logic control operation for this is performed
by the BCU.
Transfer box interlock (where fitted)
On automatic gearbox models, a transfer box interlock solenoid is controlled by the IDM to prevent transfer box shift
lever being moved out of high or low range unless certain conditions have been satisfied. The IDM controls the
operation of the transfer box relay which is located in the passenger compartment fuse box.

+ TRANSFER BOX - LT230SE, DESCRIPTION AND OPERATION, Description.
Gear position switch
A gear position switch is located on the automatic gearbox and is used to inform the BCU of the gear selector lever
position. The BCU has four sensing inputs from the gear position switch contacts W, X, Y, Z, which are used to
determine the gearbox drive status at any particular instance. The BCU gives an output corresponding to the gearbox
status derived from the gear position switch inputs. The logic states defining the gear selector positions are listed in
the table below, where Z1, Z2, Z3 and Z4 represent intermediate states which exist as the selector lever position is
changed:
Gear position Switch contacts
WX Y Z
P (Park) 1 0 0 0
Z11100
R (Reverse) 0 1 0 0
Z11100
N (Neutral) 1 1 1 0
Z21010
D (Drive) 1 0 1 1
Z31111
30111
Z40011
20001
Z40011
10010

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-19
Operation
For IDM inputs which are also inputs for BCU functions, the delay before the BCU recognises the change in input
status is less than 250 ms. The BCU uses a debounce algorithm to ignore changes in input having a duration less
than 100 ms with the exception of automatic gearbox W, X, Y, Z inputs, which have a debounce period of 33 ms.
Transit mode
To prevent excessive battery drain during transit to overseas markets, the vehicle is placed in a transit mode.
To exit the transit mode, simultaneously hold down the heated rear window switch and the rear fog lamp switch, turn
the ignition switch from 0 to II and, after a minimum of 2 seconds, release the switches.
Transit mode can be entered using TestBook. When TestBook communicates with the BCU for diagnostics related to
BCU operation, it first checks that the vehicle is not in transit mode.
Anti-theft system
The BCU uses the driver's door key lock and unlock switches to activate and deactivate the security system. The
driver's door lock is also used for entering the EKA.

+ ALARM SYSTEM AND HORN, DESCRIPTION AND OPERATION, Description.
Immobilisation
For immobilisation, the BCU disables the starter motor relay. When the engine is cranking, the ECM looks for a coded
signal from the BCU. If the signal is not received within one second of cranking, the fuel supply to the engine is
stopped and the injectors are disabled. This also prevents unburnt fuel from entering the catalyst.
If the BCU is disconnected, the engine starter motor will remain isolated by the starter motor relay and the ECM will
remain immobilised. The main wiring for the system is contained within the main harness which is relatively
inaccessible, so preventing intruders from disabling the system by cutting the wires for the immobilisation system.
Once the immobiliser has been activated, destruction of the trigger device or the wiring to it will not disarm the system.
The RF transmitter communicates to the BCU via the RF receiver using a 70 bit code. Pressing the unlock button on
the transmitter will re-mobilise the vehicle. The RF transponder is integrated into the metal key assembly, inserting
the key into the ignition switch will induce a signal in the exciter coil to re-mobilise the vehicle.
Anti-theft alarm
The alarm system provides a warning of unauthorised access to the vehicle and includes perimetric and volumetric
monitoring under the control of the BCU.
The perimetric protection system detects opening of all doors, tail door and bonnet and will also detect the operation
of the ignition key switch. The following conditions must be satisfied before the BCU will operate all of the functions
of perimetric protection:
lAll doors and hinged panels are in the closed position.
lIgnition key out of the ignition switch.
lInertia switch is not tripped.
If all conditions are not satisfied the BCU will enter a mislock condition.
The volumetric sensor uses two ultrasonic sensors mounted in the headlining to detect movement within the vehicle.
The alarm will trigger when the sensor signals the BCU for 200 ms or greater. Within a single setting period the alarm
system will allow a maximum of 10 triggers as a result of any combination of sensor inputs. It is possible to lock the
vehicle without enabling the volumetric alarm by using the key. The same conditions needed to satisfy enabling of the
perimetric protection system is also needed to enable volumetric protection.
When the alarm system is set the BCU checks the status of all the inputs from the door and bonnet switches to ensure
the integrity of the vehicle before setting the alarm system into operational mode. In some markets, when the alarm
is set the BCU sends a signal to the IDM which will cause the direction indicators to flash three times for a duration of
3 seconds.
If the sensors are triggered the BCU will activate an alarm sounder to provide an audible warning of a theft attempt.
The activation period of the alarm sounder is 25 to 30 seconds. The duty cycle of the alarm sounder is 50:50 ± 10%.

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-21
Security system status LED
The LED flashes when the anti-theft system has been set. There are four different flash rates dependent on mode of
operation or other system information.
Central door locking
The doors can be locked by the following methods:
lPressing the lock button on the remote transmitter.
lLocking the vehicle from the driver's door with the key.
lPressing the lower half of the central door lock switch.
lPushing the sill button down (will only lock that particular door).
lBy driving over 7 km/h (4 mph) – ( if the speed related locking function has been enabled).
The BCU will prevent locking if the logical conditions for locking are not satisfied. Conditions which will prevent door
locking include:
lDriver's door open.
lIgnition switch on.
lInertia switch tripped.
lVehicle is already superlocked.
A mislock may occur if the logical conditions are not met.
The doors can be unlocked by the following methods:
lPressing the unlock button on the remote transmitter
lUnlocking the vehicle from the driver's door with the key.
lPressing the upper half of the central door locking switch (not operational if the vehicle is superlocked).
lPulling the interior door handles (not operational if the vehicle is superlocked).
lInertia switch being triggered while the ignition is on and the security system is de-activated.
The BCU supplies information via the serial data bus to the IDM to energise the coil of the relays for each of the door
lock actuators.
The BCU normally checks the following inputs to determine lock/ unlock requirements:
lUnlock request.
lLock request.
lSuperlock request.
lSingle point entry request.
lLock passenger and rear doors request.
The following outputs are generated by the BCU dependent on the prevailing logic conditions and the input requests
the BCU has detected:
lUnlock all doors enable.
lLock passenger and rear doors enable.
lSuperlock all doors enable.
lLock driver's door enable.
All lock/ unlock pulses have a duration of 800 ms.
Input/Output logic for door lock/unlock
To determine if the vehicle speed is appropriate for enabling speed related locking, the BCU uses the vehicle speed
signal supplied over the serial data bus from the instrument pack.
Output/Request Superlock all
doors enableUnlock all doors
enableLock driver's
door enableLock passenger
and rear doors
enable
Unlock request 0 1 0 0
Lock request 0 0 1 1
Superlock request 1 0 1 1
Single point entry request 0 1 0 1
Lock passenger and rear doors request 0 0 0 1

BODY CONTROL UNIT
DESCRIPTION AND OPERATION 86-3-23
A timeout function is included which allows the windows and sunroofs to be operated for a period of 44 ± 1 seconds
after the ignition key has been removed from the ignition switch. The timeout function will be cancelled if the BCU
detects the following conditions:
lThe driver's door has been closed after the ignition has been switched off.
lAny door open after the ignition is switched off.
The preconditions are programmed into the BCU dependent on market specification.
The BCU does not directly control rear window operation, but it can request the IDM to remove the power feed to the
rear windows. The IDM enables power supply to be provided to the rear lift relay in the passenger fuse box. When the
relay coil is energised the relay contacts close and power is applied to the rear window motor. If the window lift
isolation switch located in the centre console is latched out, the earth path from the LH and RH rear door window
switches is broken and operation of the rear window motors through the use of the rear window switches is prevented.
Rear window operation using the console switches is not affected by the isolation switch.
In the event of a communications link failure occurring while rear window enable is on, the relay remains on until the
ignition switch is turned to the off position.
Heated screens
The heated screen time-outs and logical operations are controlled by the BCU.
Heated front screen
The BCU provides an output to the heated front screen relay and a 'heated front screen active signal' for the heated
front screen warning lamp. The BCU uses the status of the following inputs to determine the appropriate logical
operations for this feature:
lIgnition state.
lEngine running (link from instrument pack).
lHeated front screen selected (non-latched button pressed).
If the ignition switch is not in position II, or the engine running signal is OFF, the heated front screen will not be active.
The heated front screen operation period and voltage supply is controlled by the BCU. The BCU receives a voltage
supply feed from the engine compartment fuse box and an ignition switched supply through a fuse in the passenger
compartment fuse box. When the heated front screen switch is operated, it completes a path to earth, signalling a
request for heated screen operation to the BCU. The BCU then supplies a feed to the heated front screen switch to
light the switch indicator, and earths the supply from the coil of the heated screen relay to turn the heated front screen
on. The BCU maintains a supply for a predetermined time (5 minutes), then opens the earth path after the time out
period to turn the heated screen off. During the timeout period, if the heated front screen switch is pressed a second
time, the circuit is also interrupted to turn off the supply to the heated front screen.
On vehicles fitted with air conditioning, the heated front screen is also operated by the ATC ECU when DEF (defrost)
is selected. In this case the ATC ECU provides the trigger signal to the BCU to turn the heated front screen circuit on
or, if it is already on, to re-start the time out period.

+ AIR CONDITIONING, DESCRIPTION AND OPERATION, Description.
In the event of a communications link failure occurring while the heated front screen relay is on, the relay and lamp
will remain on until the ignition switch is turned off or the time-out period elapses or the heated front screen switch is
pressed.
Heated rear window
The heated rear window will only function when the engine is running, and is operated by a non-latching switch on the
instrument pack cowl.
The BCU provides a 'heated rear window enable output' and a 'heated rear window active warning lamp signal' based
on the logic status of the following inputs:
lIgnition state.
lEngine running (link from instrument pack).
lHeated rear window selected (non-latched button pressed).
If the ignition switch is not in position II, or the engine running signal is OFF, the heated rear window will not be active.